The purpose of the proposed work is to investigate various aspects of parotid acinar cell secretory activity in the adult rat by administering DL-ethionine, a competitive inhibitor of the essential amino acid methionine, which selectively affects the parotid gland acinar cells. Young rats are placed on the protein free diet and given daily injections of ethionine. Morphologic and biochemical alterations are studied at the end of intoxication period and during the immediate recovery period. Morphologic (ultrastructural) investigations will study the following areas; 1. The morphologic appearance of the intoxicated gland. 2. Events related to glandular recovery. 3. The origin and fate of the 'crystalloid'. Biochemical studies will attempt to determine: 1. The composition of the secretory granules. 2. The composition of the 'crystalloid'. 3. The effect of ethionine injection on energy producing nucleotides. Radioisotopic investigations will study: 1. The extent of acinar cell recovery from ethionine. 2. The mode of formation of the crystalloid.